The present invention relates generally to a method of making an optical fiber, and methods for fabricating optical fiber preforms, core canes and other precursor elements for making optical fiber. More particularly, the present invention relates to a method for protecting an optical fiber preform or a glass precursor element to an optical fiber preform.
Methods for making consolidated high-purity glass preforms which may be drawn into optical fiber are well known in the art. Some of the more familiar methods of making such preforms are by flame hydrolysis processes such as the outside vapor deposition process (OVD), modified chemical vapor deposition process (MCVD), vapor axial deposition (VAD) and plasma chemical vapor deposition process. These techniques and combinations thereof are commonly employed to form an optical fiber preform having a core portion and a cladding portion, the core portion having refractive index increasing dopants and/or the cladding having index of refraction decreasing dopants so that the overall refractive index of the cladding is lower than that of the core.
In one OVD method for making optical fiber, the core portion of the soot preform is first formed by introducing various gasses in predetermined amounts into a burner flame. This introduction produces oxides that may include, for example, silicon oxide and germanium oxide. These oxides deposit on a rotating mandrel until the appropriate or desired diameter core portion is reached. The oxides may be introduced in various percentages, as desired, to produce various core refractive index profiles. Once the appropriate core portion has been formed, the mandrel with deposited soot which will make up at least a portion of the core is removed from the OVD lathe. Typically, a handle portion is included on the preform and is integral therewith. The mandrel is then removed from the preform thereby leaving a soot preform having an aperture extending along its axial length and positioned at the preform""s centerline.
Next, the soot preform is inserted in a consolidation furnace. First, chlorine gas is included within the muffle portion of the furnace to aid in water removal from the preform. The preform is then heated at a high temperature (generally in the range of between about 1250xc2x0 C. to about 1700xc2x0 C., depending upon preform composition) until the deposited soot transforms into a solid, high-purity glass having superior optical properties.
Once the preform is consolidated, it is drawn, typically under a vacuum, to close the centerline aperture and stretch the preform into a smaller diameter core cane of constant diameter as is know to those of skill in the art. The core cane is drawn to a smaller diameter and cut into segments, each of which is then typically overclad with SiO2 soot to an appropriate diameter and again consolidated thereby resulting in an optical fiber preform which is fully consolidated, high optical quality glass. The resulting optical fiber preform is then transferred to a draw furnace to draw the optical fiber.
As used herein, core cane is any solid (i.e., no centerline hole therein) glass precursor element having at least a portion of the core region of what will become the optical fiber, and onto which at least additional cladding, and perhaps additional core material, must be added to form the finished optical fiber preform. Such additional core material may be deposited onto the core cane prior to the cladding being deposited, or various other process steps could be employed, such as so called rod and tube type process steps, to achieve a core cane having a desired refractive index profile across the resultant optical fiber preform. For example, the core cane can alternatively be sleeved with a tube having a desired refractive index profile, after which the core cane/tube assembly can be consolidated and drawn into a second core cane prior to deposition of the final cladding layer.
One of the problems encountered during any process which is employed to make optical fiber preforms, is that dust present in the plant atmosphere can accumulate on the various glass precursor elements used to arrive at a final optical fiber preform. Such dust may include refractory elements from the various furnaces that are present in the plant, as well as various materials that are brought into the plant from the outside atmosphere. This can be a very serious problem, as the presence of a refractory particle can and will cause breaks to occur in the fiber during the fiber draw process. Not only can these dust particles deposit onto completed optical fiber preforms, which has been consolidated into glass, but they also tend to accumulate on any of the various precursor elements such as core canes, glass tubes, or other intermediate precursor glass elements which are employed to arrive at a final optical fiber preform. This problem is only exacerbated by the fact that the glass tubes very often carry a static charge, which will attract such dust particles from the plant atmosphere.
In accordance with the invention, an improved method is provided for manufacturing a consolidated glass optical fiber preform. In one aspect of the present invention, a substrate for soot deposition and/or a glass precursor article for use in the manufacture of an optical fiber waveguide is produced and, prior to converting the glass article into a fiber, the substrate and/or glass article is stored in a protective bag to protect it from accumulating dust from the plant atmosphere. The precursor element may be any glass or soot precursor to an optical fiber preform, such as, for example, a core cane, a soot body waiting to be consolidated, a glass tube, and so forth. Most preferably, to prevent damage to the glass precursor element, the glass precursor element is consolidated into glass (rather than glass soot) prior to being inserted into the protective bag. Alternatively, the protective bag can be used to protect substrates onto which soot deposition is to take place, such as, for example, alumina and other ceramic bait rods or mandrels that are used in outside vapor deposition processes.
Preferably the protective bag contains an antistatic additive, which most preferably is an internal antistatic additive which is introduced to the bag prior to completion of the manufacture of the bag. For example, the bag may be formed using an extruding step and the antistatic additive added prior to the extruding step. One preferred material for making the bags is polyolefin based materials, e.g. polyethylene.
The protective bag is particularly advantageous in protecting complete, fully consolidated optical fiber preforms, which are ready to be drawn into an optical fiber. Very often, such optical fiber preforms are stored for a period of time in the plant before they are drawn into an optical fiber. Alternatively, the optical fiber preforms may be shipped to another location or even to another manufacturer, to be drawn into optical fiber. During the period of time between completion of the consolidated optical fiber preform and drawing of the preform into optical fiber, the protective bag protects the optical fiber preform from accumulating dust from the plant or outside atmosphere. However, the invention is not limited to protecting optical fiber preforms, and instead can be used to protect any glass precursor article employed in the manufacture of an optical fiber preform. For example, glass rods, core canes, or glass tubes which are to be employed using manufacturing techniques known in the art to combine these glass articles into a fully complete optical fiber preform, all can be protected using the protective bags discussed herein. The method in accordance with the invention minimizes the accumulation of dust on glass precursor elements employed in the manufacture of optical fiber preform.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide and overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.